How do i find out recomended rpm's ??

[twintrades]

Hey im just trying to find out what the recomended rpm's would be for my engine. So i dont over rev it trying out props. Also i cant use tilt trim right now so itll just be full down.

Its a 1979 marktwain i/o with a 165 hp mercruiser straight 6.

I dont need factory exact specs. Just around what i should be running. It has a bad 21 pich prop on now. Im thinking of switching to a 19 for better hole shot. And water sport pulling power.

So how in the wold do you find specs ??

 

[Don S]

Re: How do i find out recomended rpm's ??

Prop it to run between 3900 to 4300rpm, and normal load and trimmed properly.
Best to prop it in the upper part of the range, then when loaded heavier you are still not lugging the engine.

 

[ziggy]

Re: How do i find out recomended rpm's ??

^
what he said....

fwiw. on my 165hp L6 in my 19' boat i run a 19p aluminim. it came with a 21p alum.and i could barely reach the bottom of wot spec. (listed above) trimmed pretty far out. with the 19p i hit 4300 with my normal load and trim..
when i was a kid and water skiing. dad's 16' trisonic had a 165hp L6 in it. we ran a 17p alum. since we were big into water skiing. the 17p could easy reach wot spec. so had to be a little cool when we weren't pulling skiers.. but the hole shot was great for the duty we gave that boat..

imho be carefull if yer switching to a ss prop. our 1 drives have the o ring groove at the top of the lower drive shaft. it's a prime place for the shaft to snap off if ya hit an uso... ss don't give much. alum. hopefully breaks off a prop blade instead of the drive shaft. hopefully...